Coaxial connector



March 5, 1968 M. F. OKEEFE ET AL COAXIAL CONNECTOR 2 Sheets-Sneet 1 Filed Sept. 10, 1965 VENTOR. MICHAEL FRA 5 QKEEFE \louu (HANG-7415M FAN BY WMM W4 M. F. O'KEEFE ET AL COAXIAL CONNECTOR 2 Sheets-Sneet 2 INVENTOR. MI HAEL FRANCIS Q'KEEF: 4mm CHANG-NIEN FAN BYQ LQ Q- 3W March 5, 1968 Filed Sept. 10, 1965 United States 3,372,364 COAXIAL CONNECTOR Michael Francis OKeefe, Mechanicsburg, and John Changnien Fan, New Cumberland, Pa., assignors to AMP Incorporated, Harrisburg, Pa.

Filed Sept. 10, 1965, Ser. No. 486,360 12 Claims. (Cl. 339-177) ABSTRACT OF THE DISCLOSURE A coaxial connector device is disclosed including a double-ended receptacle and a mating plug structure. The plug structure includes a conductive shell having a smooth bore with a slight taper carrying a dielectric insert compressively loaded against axial pullout by the slight taper to axially lock a center contact member therein. The contact member has a substantially constant outer diameter but includes a series of slight serrations engaged by the dielectric material of the insert in compression. The receptacle carries in the center thereof a dielectric insert carrying a center contact member locked against axial displacement by thin wedge fitted rings within the shell on either side of the insert. The mating portions of the receptacle and plug are held of a substantially constant diameter.

Background of the invention One of the problems which has plagued the designer and user of connectors for coaxial cable is center contact float. This problem arises whether the center contact is soldered to the cable center conductor or is crimped thereto and manifests itself most frequently by the center contact moving axially relative to the connector shell outwardly toward the entry of the cable within the connector. It is caused by axial loads placed upon the cable center conductor which are then transmitted to the connector center contact to pull it out of its supporting structure. These loads are developed in normal uses of the cable and are aggravated by change in temperature, which causes a diiferential contraction of the cable outer conductor, its dielectric sheath and the cable center conductor. The problem is also caused by relatively long spans of cable wherein the cable itself is placed in substantial tension.

Industry has attacked the problem in a number of ways including having the center contact molded into a thermosetting plastic insert and/or utilizing radially displaced flanges, shoulders, barbs and the like, which lock against a supporting dielectric insert.

Several problems arise with respect to molding a center contact in a connector. It is expensive. More importantly, the center contact is so rigidly held by the plastic as to require a relatively sloppy fit in the mating part so that a given production connector will be assured of fitting with a given production receptacle. This results in poor performance. Another problem with the molded approach is that of shrinkage which may cause the center contact to be separated from the plastic in use.

The use of a radial flange or shoulder extending outwardly from the center contact member inherently complicates connector design by creating a change in spacing between the inner and outer conductive portions of the connector and by creating abrupt edges and transverse surfaces which alter the mode of energy transfer. As a result of this connector performance in terms of VSWR is adversely affected and this is proportionate to the frequency of the signals carried by the connector. It is possible, of course, to so adjust characteristic impedance in the zone of the flange or shoulder or to insert compensa- 3,372,364 Patented Mar. 5, 1968 Free tion in such zone to minimize signal degradation. These steps are costly and with present day techniques are based upon empirical solutions which lead to performance which is at best only barely adequate.

Another problem with connectors of the prior art relates to a practice in industry of standardizing on dimensions, sizes and mateability. This has the unfortunate result in making many present day connector designs for higher frequency signal communication heir to design restrictions generated at a time when frequency requirements were lower. An example of this is in a connector which is known in the trade as a UHF connector. The UHF connector was originally designed for a maximum range of 200 megacycles but has been now incorporated for use in circuits of higher frequency requirements. Some users merely accept the sacrifice in performance which results in order to obtain the economies of this large production connector which is otherwise well accepted in the industry. Others have attempted to upgrade the connector, but as presently advised, such efforts have only extended its range to about 500 megacycles before virtual cut-off. The problem is really one of trying to deal with a dimensional limitation in a connector design where the principal means of achieving improved operation is by changes in dimension which would make the design non-standard.

Summary of the invention This invention relates to an improvement in coaxial connectors.

Accordingly, it is an object of the present invention to provide a connector design which has an improved center contact locking means which does not rely on flanges or upon solidly molded assemblies to prevent center contact float. It is another object of the invention to provide a simple and inexpensive coaxial connector which is capable of operation with low loss up to frequencies of thousands of megacycles rather than hundreds of megacycles. It is a further object of the invention to provide a novel plug and receptacle structure for coaxial connectors and the like which is capable of eflicient signal transfer in the higher frequency ranges in a simple and inexpensive structure of few components which lends itself to uses with both crimping and soldering techniques.

The foregoing problems are solved and the foregoing objects are attained in the present invention in one aspect through the use of a center contact member of substantially constant diameter having a knurling on one portion thereof adapted to be seated and held by a dielectric insert loaded in compression to bear against the knurled surface. In the preferred embodiment the insert is itself locked within the connector by a tapering of the connector shell to a slightly larger diameter in its innermost region. In a second aspect the connector of the invention is comprised of a novel plug and receptacle assembly which employs an association of metal and dielectric parts to lock the contact members of plugs and receptacle assemblies against axial displacement. These parts are supported coaxially of such assemblies and are fully compensated by appropriate removal of and shaping of dielectric material between the conductors of the assemblies.

In the drawings:

FIGURE 1 is a perspective showing the invention in a preferred embodiment including a plug half terminated to a cable and its mating receptacle;

FIGURE 2 is an exploded view of the plug half of the connector of the invention showing the various components thereof;

FIGURE 3 is an exploded view of the receptacle half of the connector of the invention showing the components thereof;

FIGURE 4 is a longitudinal section of the plug and receptacle assemblies of the invention showing the center contact locking means thereof and the compensation means therefor in detail; and

FIGURE 5 is a longitudinal section of the plug and half portions of the connector as intermated.

Description of preferred embodiment Referring now to FIGURE 1 the invention is shown embodied in a UHF plug 20 terminated to a coaxial cable and embodied in a UHF double-ended receptacle 30, which is adapted to receive the plug 20. It is this general type of connector which raises the problems above outlined and the description hereinafter to be given will be related to this specific embodiment. It is contemplated that various aspects of the invention including particularly the technique of locking the center contact member and the structure for compensation may be adapted to practically any connector assembly for coaxial devices. It is also contemplated that the universal receptacle in its detailed structure represents a teaching which may be employed by those skilled in the art in a wide variety of receptacle configurations.

The coaxial cable 10 as shown in section in FIGURE 4 is comprised of the center conductor 12 surrounded by a dielectric material sheath 14, an outer conductor braid 16 and an outer protective sheath 18. This cable construction is typical of the cable constructions employed to transmit the higher signal frequencies or to shield low level signals transmitted on the center conductor of the cable. It is contemplated that other cable constructions may be served by the invention in a manner which will be apparent to those skilled in the art following the description of the invention.

Referring now in detail to the problems solved by the invention, axial float of center contact member is caused by relative movement of the center conductor 12 of the cable which in turn pulls or drags the center contact member within its shell structure. This may occur by reason of movement of the dielectric sheath 14 within outer conductor 16 and protective sheath 18 or it may occur by movement of the center conductor 12 within sheath 14. In any event the design of a connector should be such as to prevent the connection between the center contact member and the cable center conductor from being broken or separated to a point of substantial increase in resistance or open circuit. Normally this is not diflicult and may be accomplished by a well-designed crimp of the center contact member inwardly against a substantial area of the cable center contact or even by a well prepared and well executed soldering of the center contact to the cable center conductor. An adequate locking of the center contact member to the cable center conductor, however, means that axial loads will work in a sense to pull the center contact member and cause it to be displaced from its surrounding dielectric bead insert and/ or the outer conductive shell of the connector. In the higher frequency applications the usual practice is to employ flanges, shoulders, offsets, tangs or similar holding means on the surface of the center contact member to resist pullout. But these may aggravate the problem because if there is movement of the contact member a change in spacing between inner surface of the outer shell of the connector and these holding means will invariably occur to destroy any effort toward compensation of the connector design or at least considerably reduce performance.

In one prior art device there is a center contact member having a flange thereon which extends radially at the forward end of the dielectric insert in which the center contact member is mounted. This would be at point F in FIGURE 4 of the present drawings. This flange is for the stated purpose of preventing axial float and is typical of the prior art in this respect. With respect to the present design, if a flange F were employed and if through axial loads imposed upon the center contact pin this flange were permitted to be pulled even slightly to the left relative to the shell of the connector 29 it would considerably alter the radial spacing between conductive surfaces and a distinct discontinuity to alter the mode of energy transfer in a zone which has been specially compensated. A flange located on the innermost end of the center contact member in FIGURE 4 as at F would be drawn much closer to the reduced inner diameter of the shell and would there also create a discontinuity and an alteration in the transposition of electric field lines through approximate zone of dielectric material between conductive surfaces. In many other designs wherein there are substantial relative changes in diameter in the outer conductive shell this effect would be exaggerated.

The connector plug of the invention eliminates these problems without relying upon flanges, shoulders, or radial offsets. The plug 20 includes an outer conductive shell 22 having an enlarged forward portion which on its outside forward end includes a series of threads 22a adapted to cooperate with a nut (not shown) fitted over the connector shell which extends forwardly of 22a to engage threading on a receptacle member 30. The rear portion of the shell 22 includes an integral extension 22b which has its outer surface grooved as at 22c to facilitate termination to the cable braid 16 which is carried up and over 22b as shown in FIGURE 4. As shown in FIGURES 14 there is provided a ferrule member 24 which is of malleable material and relatively thin wall section and is adapted to be crirnped inwardly to drive the cable braid 16 into a tight and stable interface with the surface of 220 and terminate the cable outer conductor to the shell 22. The ferrule 24 is made to extend back over the cable and engage the outer protective sheath 18 to support such against bending moments which may be transmitted to the contact surfaces of the outer and inner conductors and cause such to be worked loose. This portion of the ferrule 24 which overlies the cable outer protective sheath 18 is crimped inwardly under enough force to cause the ferrule to grip but not substantially deform the cable. On the forward face of the shell 22 are provided a pair of teeth 22d shown in FIGURE 1 which serve to lock the plug half of the connector of the invention against relative movement to the mating receptacle 30 by engagement with complementary V-shaped grooves in the receptacle outer shell. In the forward end of 22 is provided a bore 22:: which in a preferred embodiment tapers very slightly to an increased diameter in a sense away from the mouth of 22. Adjacent to and adjoining the bore 22e is a further bore 221 within the portion 22b which is sized to receive in an easy fit the dielectric sheath 14 of the cable. The surfaces of the bore 22] serve to support the cable through engagement with this sheath coaxially within the shell 22.

Fitted within the bore 22e is a dielectric insert 26 which substantially fills the bore and is in fact slightly compressed by the bore surfaces. The insert 26 includes a forward surface shaped as shown at 26a to provide compensation which will be discussed in greater detail hereinafter relative to FIGURE 5. Centrally of 26 is provided a bore 26b of a diameter slightly smaller than the diameter of a center contact member 28. At the rear face of 26 is provided a relief 26c which receives and supports the end of the cable dielectric sheath 14 and in turn the center conductor of the cable. This relief serves to increase the voltage breakdown path from the end of the center contact member 28 to the conductive shell member 22 and furthermore provides compensation which will be described hereinafter.

The center contact member 28, as will be seen from FIGURES 2 and 4, is substantially cylindrical, having a substantially constant diameter along its entire length. There are no outwardly projecting flanges, shoulders, or offsets as in the above-mentioned prior art. The forward and projecting part of 28 shown as a surface 28a is smooth and circular to define a contact surface for engagement with a mating surface in the receptacle 30. The part of the contact member 28 buried within 26 is as shown roughened along its length. In a preferred embodiment this surface is formed by knurling, shown as 220. Due to the diameter of 26 and the diameter of its bore 22b relative to the diameter of bore 22c, the center contact member 28 is, in the position shown in FIGURE 4, locked within the shell against axial displacement. The dielectric material of insert 26 is forced down within the roughened surface of 22c to form a network of holding and locking engagements with the surface of 28b. These various diameters are chosen to provide enough compression to lock the center contact member against axial movement up to a certain desired pull-out force with care taken to not substantially alter its dielectric constant with a resulting change in the characteristic impedance throughout the zone encompassing 220. The roughened surface defined by 22c is symmetrical and slight relative displacements within the shell due to production tolerances of the part or due to assembly and use are not critical. This is of course not the case wherein there is a definite offset which must be exactly placed in other designs.

In an actual embodiment the diameter of bore 22:: was made to be approximately 0.436 of an inch in its forward portion and 0.440 of an inch in its rearmost portion. The dielectric insert 26, was formed of polypropylene material approximately 0.441 of an inch in outer diameter having a bore 26b of 0.125 diameter. The center contact 28 was made to be 0.132 of an inch in outer diameter with its roughened surface being formed by knurling through spiraling indentations approximately 0.005 of an inch in depth. Tests of a connector utilizing these features showed it to have extremely low VSWR up to 6000 megacycles. This was somewhat surprising in view of the roughness of the surface defined by 22c, but is thought to be answered by some sort of balance achieved in the disposition of electric field lines relative to energy passing through the connector in conjunction with the other compensation provided in the connector.

The connector plug 20 has been shown and described relative to an embodiment which is adapted to be crimped with respect to the cable outer conductor and with respect to the cable center conductor. It is contemplated, however, that the invention features just described will have utility with other types of terminations of the cable conductors. For example, some threaded structure might be employed to terminate the outer conductor and solder might be employed to terminate the center conductor to the center contact member. The crimp version is, however, preferred and it is thought that the practice of crimping the center contact member forwardly of the contact member support portion 22c adds to the resulting pull-out strengthof the device. It is, in fact, known that the use of the ferrule to extend out over and crimp the cable at a point removed from the sleeve portion 22b improves this pull-out.

Turning now to the receptacle of the invention reference is made to FIGURES 1, 3 and 4. The receptacle 30 is comprised of an outer conductive metallic sleeve member 32 which has a central smooth portion 32a and on each side thereof extending outwardly portions 32b having their exterior surface threaded as shown to mate with the threading of a nut projecting from the plug to mechanically lock and hold the plug and receptacle together. At the ends of 32 are provided V-grooves 32c adapted to cooperate with the projecting teeth 22d of the plug member. The interior of 32 is defined by a smooth bore extending therealong identified by numeral 32d. In the specific embodiment described the outside diameter of 30 is standardized to an accepted dimension for such member in UHF type connectors. Other dimensions are also standardized to provide a universal mating with various similar products of various manufacturers.

Wedgefitted within the outer portions of the bore 32 are a pair of rings 34 of thin wall section each having an interior bore 34a which is equal in diameter to the bore 22c. These rings are formed of a material having the characteristics of brass and are sized in diameter so that they must be driven under substantial force within 32d to be permanently locked within 30. The inner ends of each of the members 34 form an offset which lock a dielectric insert 36 in place within the receptacle. This insert has a diameter to substantially fill the bore 32d and is made to extend along a substantial portion in order to provide a broad bearing area to support a receptacle center contact structure 38. The outer faces of 36 are shaped as shown at 36b for compensation, which will be discussed hereinafter, and there is included within 36 a central and coaxial bore 36a. The insert includes a split as best shown in FIGURE 3, to permit loading of the center contact structure 38 within the bore 36a. As shown in FIGURE 4 the insert 36 is positively locked against axial or radial displacement within 32 by the rings 34. The center contact of the receptacle 38 includes at each end a bifurcated spring portion 38a which tapers inwardly from a broadened base portion 38b. The pair of resilient fingers are separated by a center and solid portion 38a of a slightly reduced diameter which at its ends defines a face to bear against the insert material and lock the center contact 38 against axial displacement.

As thus described the invention comprises a plug and receptacle forming an assembly of few parts and of a generally rugged construction. The assembly is adapted to hold the center contact members exactly against radial displacement relative to the outer conductive portions of the connector. The plug and receptacle mating is shown in FIGURE 5.

Also in FIGURE 5 there is shown electrical compensation which provides efiicient energy transfer through the plug-receptacle assembly. Assuming that the device shown is for 5082 cable, the following treatment is given. Beginning to the left of I it will be apparent that the diameters of the conductors and the dielectric material are such as to provide a characteristic impedance equal to that of the cable. In zone I there is a necessary change in inner and outer diameters, but this is compensated to have a characteristic impedance equal to approximately 509 by the choice of spacing between conductive surfaces and the composite dielectric path traversed by the signal electric field. In the zone II the characteristic impedance is also made to be approximately 509 by virtue of the diameters of the bore 222 and the outer diameter of the center contact pin portion 220. The dielectric insert is in an actual embodiment made of polypropylene. The very slight tapering of the bore 22e provided in a preferred embodiment to lock the dielectric pin assembly within the shell'has not been found to appreciably reduce the efficiency of the connector. In the zone III there is again a characteristic impedance of 509 provided through a composite dielectric path including the dielectric material insert and air. In the zone IV, as will be discerned, there is no solid dielectric but rather an air space extending between the conductive surfaces of the outer and inner portions of the receptacle. By providing air extending along the intermating portions of the center contact members the desired characteristic impedance of 509 is not only achieved but the center contact members are left free for slight movement to accommodate mating without any need for support by the dielectric material. This contrasts with prior art devices which have a rigid molded plastic dielectric insert in the zone overlying the receptacle center contact members. In the next zone the dielectric material is in a preferred embodiment, Teflon and air, and the section has a characteristic impedance approximately equal to 5062. The zone V includes a specialized compensation to the shaping of the dielectric material in accordance with U.S. application Serial No. 395,150 by John C. Pan, filed September 9, 1964. The electric field passing through the zone V is affected in a manner as described in such application minimizing signal loss and distortion. Zone V1 is solid Teflon with the change in diameters adjusted to a characteristic impedance of 509.

As previously mentioned, the various features of the invention may be incorporated in different coaxial connectors, receptacles, plugs, jacks and the like.

Having now described our invention in a preferred form in order to enable its practice by those skilled in the art, we now define it through the appended claims.

What is claimed is:

1. In a connector device for coaxial cable of the type having a center conductor surrounded by dielectric material and an outer conductor, a connector plug and a mating receptacle, said connector plug including an outer conductive shell adapted to be terminated to the cable outer conductor, said shell including a forward bore free of inward projections and substantially smooth along its length and having a slight taper increasing from the forward end thereof along the length thereof, a dielectric insert fitted within said shell bore and at least One center conductive contact member fitted within said insert and adapted to be connected to the cable center conductor, the said center contact member having a first portion free of said insert extending out of said shell for mating engagement with a contact in said receptacle and having a second portion of a diameter similar to that of the said first portion, said second portion having a roughened outer surface, the said insert and second portion being sized relative to said shell bore with said insert being compressively loaded by engagement with the bore surface to bear against said roughened surface to lock the center contact against axial movement relative to said connector shell, the said contact member and the said bore having diameters along the length thereof which are substantially constant whereby to maintain a substantially constant characteristic impedance matched to the characteristic impedance of the cable of use.

2. The device of claim 1 wherein said roughened surface is formed of indentations in the said second portion which are of substantially symmetrical configuration as viewed from a cross-section of said second portion.

3. The device of claim 1 wherein said roughened surface is formed of indentations which are of a depth slight as compared to the radial space between the said shell member and the said second portion.

4. The device of claim 1 wherein the said roughened surface is defined by a knurling of slight depth in the surface of said second portion.

5. The device of claim 1 wherein the said second portion is in axial length a significant part of the overall length of said center contact member whereby to provide a substantial bearing area to resist movement of said contact member.

6. The device of claim 1 wherein the said insert is formed of a thermoplastic material.

7. In a connector device for coaxial cable of the type having a center conductor surrounded by a dielectric material and an outer conductor, a connector plug and mating receptacle, said plug having an outer conductive shell adapted to be terminated to the cable outer conductor and including a forward bore, a single dielectric insert fitted within said shell, at least one center conductive contact member fitted within said insert and adapted to be connected to the cable center conductor, the said contact member having a first portion free of said insert to define a surface for contacting with a mating receptacle contact member and having a second portion having an outer surface carrying a series of serrations, the said shell having a forward bore which tapers to an increasing diameter from the opening of said shell, the said insert being Wedge-fitted to be locked within said tapering surface and being sized relative to said bore whereby to be driven in compression to lock said insert and said center contact member within said shell, the said forward bore taper and the said contact member second portion having diameters substantially constant along the length thereof to maintain the characteristic impedance along the length of said forward bore substantially constant,

8. The device of claim 7 wherein the said shell has a rear portion adapted to be fitted within the outer conductor of said cable and there is included a ferrule member adapted to be deformed over said rear portion to lock the outer cable to the said rear portion and terminate the outer conductor to the shell of the cable.

9. In a coaxial assembly for cable of the type having a center conductor surrounded by dielectric material and an outer conductor including a connector comprised of a conductive shell having a rear portion adapted to receive the cable outer conductor, means to terminate the outer conductor to said portion, a first bore through said shell to receive the cable dielectric material and cable center conductor, a second bore having a slight taper increasing for the mouth of said shell and free of inward projections to define a substantially smooth surface extending therealong, a thermoplastic insert in said second bore, a diameter to be compressively loaded and thereby locked to said shell, a center conductive contact member including a portion of roughened outer surface engaged by the material of said insert in compression to be locked to said insert and extending outwardly of said shell, the said member being of a substantially constant diameter along the length thereof whereby the radial path between the surface of the second bore and the surface of said portion of the contact member is substantially constant along the said bore to provide in conjunction with said dielectric material a given and substantially constant characteristic impedance, a receptable comprised of a second conductive shell including in the center thereof a second dielectric insert with ring means disposed on either side of said insert Wedge fitted for permanent retention in said shell and extending outwardly to the end of said shell to lock said insert in said shell, a second center conductive contact member in said insert projecting outwardly to the end of said shell and adapted to mate with the connector center contact member, the major interior portion of said second shell surrounding said second contact member being comprised of air as a dielectric material, the interior diameter of said ring means and the outer diameter of said second center conductive contact member being dimensioned to provide a substantially constant radial dimension along the length thereof when the first mentioned contact member is fitted in the said second mentioned contact member which, taken in conjunction with the dielectric medium in said receptacle provides a characteristic impedance substantially constant along the length thereof and equal to the said given characteristic impedance, the said connector and receptacle being sized to provide a mating of the outer and inner conductive portions to extend the coaxial path of said cable.

10. The assembly of claim 9 wherein the characteristic impedance of the cable is maintained throughout the length of the connector and receptacle.

11. In a coaxial device, a coaxial cable connector and a receptable receiving and connecting with said coaxial cable connector, said receptacle having a thin outer conductive shell with means externally disposed on at least one end to facilitate mechanical engagement to said connector, a dielectric insert positioned in said shell and a center contact member carried in said insert coaxially of the interior of said shell and extending therealong for a substantial portion of the shell length free of said insert, a relatively thin walled ring wedged within said shell to lock said insert and said center contact therein against axial displacement, said ring having an interior diameter approximating the forward interior diameter of the said connector.

12. In a coaxial device, a coaxial connector and a receptacle receiving and connecting said coaxial connector at either end thereof, said receptacle being comprised of a thin conductive shell. having externally disposed thereon means to facilitate mechanical engagement to a said connector, a dielectric insert positioned in the center of said shell, relatively thin ring members of an outer diameter to be wedged within said shell and permanently secured therein from opposite ends of said shell to lock said insert Within said shell and of a length to reside within said shell, a center contact member held in the said shell center within said insert and projecting free of said insert outwardly within said rings, said contact member being adapted to engage the center contact member of said connector to complete a coaxial connection through said receptacle.

References Cited UNITED STATES PATENTS Fisher 339-21 Couty 285-3842 X Stevens 339-59 X Felts 339-177 X Edlen et al 339-177 X Colussi 339-177 X Stark et a1. 339-177 MARVIN A. CHAMPION, Primary Examiner. I. R. MOSES, Assistant Examiner. 

